Saw chain used for cutting concrete suffers unique wearing problems. Unlike wood cutting which primarily removes wood material in the form of chips, concrete cutting removes material by abrasion in the form of minute particles referred to as fines. If uncontrolled, the fines envelope the entire surrounding and permeates through the tiniest cracks and crevices. Control of the fines is achieved using copious amounts of water under pressure. Water is flowed through the saw chain and captures the fines to become a slurry. The water also provides cooling of the work tools and work surface as the abrasion form of cutting generates extreme heat.
A particular problem experienced by saw chain is that the saw chain is constructed of numerous individual links, center links and side links, pivotally connected together by rivets. Each link is provided with a front and rear rivet hole and a rear hole of a center link is aligned with the front holes of a pair of following side links, and the front hole of the center link is aligned with the rear holes of a pair of leading side links. Rivets projected through the aligned holes join the links together and the sequence is repeated throughout to form a desired loop of saw chain. The loop is mounted on a guide bar and drive sprocket and travels in a substantially oval path.
As the individual links travel around the defined oval path, the links pivot relative to each other particularly when traversing the ends. The substantial drive power necessary to drive the saw chain is imparted by the drive sprocket whose teeth are designed to fit between successive center links and engages the rear edges of the center links.
The problem to which the present invention is directed is the wearing of the chain due to the pivoting action. The rivets are clamped to the side links so that the bearing surfaces, i.e., where relative movement takes place, is the cylindrical surface of the rivets and the engaged inner walls surrounding the rivet holes of the center links.
Even though the center links and side links fit closely together, the slurry of fines and water gets into and between the bearing surfaces and accelerates wearing. To reduce such wearing, the water pressure is increased, e.g., to 100 psi to maintain a high rate of flow of water which at least partially reduces the abrasive action of the slurry (fines admixed with the water).
The 100 psi water pressure itself causes problems as it is not readily available at many job sites. Furthermore, wearing is still excessive. Such wearing causes chain stretch to the point where the sprocket no longer properly fits between the center links causing a further wearing problem. In combination, the wearing prematurely reduces the life of the chain far sooner than what can be provided as the cutting teeth life.